In England and Wales, marriage at the age of 16 or 17 was previously allowed with parental consent. With a new law, the legal age of marriage was raised to 18.
The government said this would help protect children.
Forced marriage used to be a crime only if threatened. Now, however, it has become illegal for children to marry, either by force or without coercion.
According to the news of the BBC, Violators of the new regulation face up to seven years in prison.
This change does not apply in Scotland and Northern Ireland, where the legal age of marriage is 16. Parental consent is required for marriages under the age of 18 in Northern Ireland, while in Scotland there is no such requirement.